Researchers use seaweed to manufacture raw materials for civil construction
The accumulation of these algae on beaches can harm health, tourism, fishing, and biodiversity. They are usually collected and disposed of in landfills, but a study by Brazilian researchers has found a use for the biomass: to produce lightweight ceramic
Fundação de Amparo à Pesquisa do Estado de São Paulo
image:
Large quantities of brown algae have been washing up on beaches in northern Brazil, the Caribbean, and the United States
view moreCredit: João Adriano Rossignolo/FZEA-USP
Brazilian researchers have developed a ceramic clay that is lighter than that normally used in civil construction by adding algae from the Sargassum genus to the manufacturing process.
These brown algae, also known as sargassum, are common in the central Atlantic Ocean. However, they have been washing up in large quantities on beaches in the Caribbean, the United States, and northern Brazil, where they have become problematic. Their accumulation on beaches can harm human health due to the gases emitted during decomposition, as well as damage tourism, fishing, and local biodiversity.
“Normally, sargassum is collected and disposed of in landfills without any practical use. That’s why we decided to research a way to take advantage of this large amount of biomass on the beaches,” says João Adriano Rossignolo, a professor at the Department of Biosystems Engineering at the School of Animal Science and Food Engineering of the University of São Paulo (FZEA-USP) who coordinated the study.
In partnership with researchers from the Federal University of São Carlos (UFSCar), the USP group tested using algae in the manufacture of ceramic clays, used in construction to reduce the weight of concrete, in slabs to improve thermal comfort, and in gardening. The research was supported by FAPESP.
Sargassum was incorporated into the samples at proportions of 20% and 40%, as well as 0% for comparison. The samples were molded and sintered – a process that compacts clay using heat to make it solid – at temperatures of 800 °C, 900 °C, and 1,000 °C in conventional and microwave ovens.
Once the materials were ready, several tests were performed to evaluate factors such as water absorption, porosity, and compressive strength. Additionally, a comparison was made between the life cycle of conventional expanded clay and the different formulations with added sargassum, a methodology that assesses the environmental impacts of a product from raw material extraction to final disposal.
The results, published in the Journal of Materials in Civil Engineering, indicate that adding sargassum reduced the apparent density of lightweight ceramic clay aggregates, particularly at a concentration of 40%. However, only materials sintered in a microwave oven met the strength requirements at all temperatures. In terms of life cycle, the versions with sargassum performed better environmentally than conventional expanded clay.
This led the researchers to conclude that lightweight ceramic clay aggregates with microwave-sintered sargassum are a viable alternative to mitigate the damage caused by the large amount of algae on the coast. This alternative reduces the consumption of natural resources and increases energy efficiency.
In addition to this work, the team evaluated the feasibility of using algae to produce particulate panels for the furniture and construction industries, as well as fiber cement tiles. They used sargassum ash as a substitute for limestone. “The results were surprising, as we were able to use 30% sargassum in the panels and replace 100% of the limestone with its ash, with results that fully comply with current standards for these products and improve the durability and mechanical properties of the materials,” says Rossignolo.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
Journal
Journal of Materials in Civil Engineering
Article Title
Life Cycle Assessment of Lightweight Ceramic Clay Aggregates Sintered in a Microwave Oven with the Incorporation of Sargassum spp. Particles
FAU tells ‘story’ of Atlantic’s sargassum surge using 40 years of data
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Brian Lapointe, Ph.D., emerges from sargassum in Little Palm Island in June 2014.
view moreCredit: FAU Harbor Branch
Researchers at Florida Atlantic University’s Harbor Branch Oceanographic Institute have released a landmark review tracing four decades of changes in pelagic sargassum – free-floating brown seaweed that plays a vital role in the Atlantic Ocean ecosystem.
Once thought to be primarily confined to the nutrient-poor waters of the Sargasso Sea, sargassum is now recognized as a rapidly growing and widely distributed marine organism, whose expansion across the Atlantic is closely linked to both natural processes and human-induced nutrient enrichment.
The review, published in the journal Harmful Algae, sheds new light on the origins and development of the Great Atlantic Sargassum Belt, a massive recurring bloom of sargassum that stretches across the Atlantic Ocean from the coast of West Africa to the Gulf of America.
Since its first appearance in 2011, this belt has formed nearly every year – except in 2013 – and in May, reached a new record biomass of 37.5 million tons. This does not include the baseline biomass of 7.3 million tons historically estimated in the Sargasso Sea.
By combining historical oceanographic observations, modern satellite imagery, and advanced biogeochemical analyses, this review provides a comprehensive framework for understanding the dramatic changes in sargassum distribution, productivity and nutrient dynamics. It also highlights the broader implications of anthropogenic nutrient enrichment on ocean ecology and the need for coordinated international efforts to monitor and manage the impacts of these massive seaweed blooms.
“Our review takes a deep dive into the changing story of sargassum – how it’s growing, what’s fueling that growth, and why we’re seeing such a dramatic increase in biomass across the North Atlantic,” said Brian Lapointe, Ph.D., lead author and a research professor at FAU Harbor Branch. “By examining shifts in its nutrient composition – particularly nitrogen, phosphorus and carbon – and how those elements vary over time and space, we’re beginning to understand the larger environmental forces at play.”
Early in the review, Lapointe and co-authors Deanna F. Webber, research coordinator; and Rachel Brewton, Ph.D., an assistant research professor, both with FAU Harbor Branch, explain that early oceanographers charted the Sargasso Sea based on surface sightings of sargassum, believing the seaweed thrived in its warm, clear, but nutrient-poor waters. However, this notion created a paradox when mid-20th-century oceanographers described the region as a “biological desert.”
However, recent satellite observations, ocean circulation models, and field studies have resolved this paradox by tracing the seasonal transport of sargassum from nutrient-rich coastal areas, particularly the western Gulf of America, to the open ocean via the Loop Current and Gulf Stream. These findings support early theories by explorers who proposed that Gulf-originating sargassum could feed populations in the Sargasso Sea.
Remote sensing technology played a pivotal role in these discoveries. In 2004 and 2005, satellites captured extensive sargassum windrows – long, narrow lines or bands of floating sargassum – in the western Gulf of America, a region experiencing increased nutrient loads from river systems such as the Mississippi and Atchafalaya.
“These nutrient-rich waters fueled high biomass events along the Gulf Coast, resulting in mass strandings, costly beach cleanups and even the emergency shutdown of a Florida nuclear power plant in 1991,” Lapointe said. “A major focus of our review is the elemental composition of sargassum tissue and how it has changed over time.”
Laboratory experiments and field research dating back to the 1980s confirmed that sargassum grows more quickly and is more productive in nutrient-enriched neritic waters than in the oligotrophic waters of the open ocean. Controlled studies revealed that the two primary species, sargassum natans and sargassum fluitans, can double their biomass in just 11 days under optimal conditions. These studies also established that phosphorus is often the primary limiting nutrient for growth, although nitrogen also plays a critical role.
From the 1980s to the 2020s, the nitrogen content of sargassum increased by more than 50%, while phosphorus content decreased slightly, leading to a sharp rise in the nitrogen-to-phosphorus (N:P) ratio.
“These changes reflect a shift away from natural oceanic nutrient sources like upwelling and vertical mixing, and toward land-based inputs such as agricultural runoff, wastewater discharge and atmospheric deposition,” said Lapointe. “Carbon levels in sargassum also rose, contributing to changes in overall stoichiometry and further highlighting the impact of external nutrient loading on marine primary producers.”
The review also explores how nutrient recycling within sargassum windrows, including excretion by associated marine organisms and microbial breakdown of organic matter, can sustain growth in nutrient-poor environments. This micro-scale recycling is critical in maintaining sargassum populations in parts of the ocean that would otherwise not support high levels of productivity.
Data from sargassum collected near the Amazon River mouth support the hypothesis that nutrient outflows from this major river contribute significantly to the development of the GASB. Variations in sargassum biomass have been linked to flood and drought cycles in the Amazon basin, further connecting land-based nutrient inputs to the open ocean.
The formation of the GASB appears to have been seeded by an extreme atmospheric event – the negative phase of the North Atlantic Oscillation in 2009 to 2010, which may have helped shift surface waters and sargassum from the Sargasso Sea southward into the tropical Atlantic.
However, the researchers caution that there is no direct evidence of this movement. Moreover, genetic and morphological data suggest that some sargassum populations, particularly the dominant S. natans var. wingei, were already present in the tropical Atlantic prior to 2011, indicating that this region may have had an overlooked role in the early development of the GASB.
“The expansion of sargassum isn’t just an ecological curiosity – it has real impacts on coastal communities. The massive blooms can clog beaches, affect fisheries and tourism, and pose health risks,” said Lapointe. “Understanding why sargassum is growing so much is crucial for managing these impacts. Our review helps to connect the dots between land-based nutrient pollution, ocean circulation, and the unprecedented expansion of sargassum across an entire ocean basin.”
This work was funded by the Florida Department of Emergency Management, United States Environmental Protection Agency, South Florida Program Project, and the NOAA Monitoring and Event Response for Harmful Algal Blooms program. Historical studies included within the review were funded by the NASA Ocean Biology and Biogeochemistry Program and Ecological Forecast Program, NOAA RESTORE Science Program, National Science Foundation, “Save Our Seas” Specialty License Plate and discretionary funds, granted through the Harbor Branch Oceanographic Institute Foundation, and a Red Wright Fellowship from the Bermuda Biological Station.
- FAU -
Sargassum on a beach in Palm Beach County in 2021.
About Harbor Branch Oceanographic Institute:
Founded in 1971, Harbor Branch Oceanographic Institute at Florida Atlantic University is a research community of marine scientists, engineers, educators, and other professionals focused on Ocean Science for a Better World. The institute drives innovation in ocean engineering, at-sea operations, drug discovery and biotechnology from the oceans, coastal ecology and conservation, marine mammal research and conservation, aquaculture, ocean observing systems and marine education. For more information, visit www.fau.edu/hboi.
About Florida Atlantic University:
Florida Atlantic University serves more than 32,000 undergraduate and graduate students across six campuses located along the Southeast Florida coast. It is one of only 21 institutions in the country designated by the Carnegie Classification of Institutions of Higher Education as an “R1: Very High Research Spending and Doctorate Production” university and an “Opportunity College and University” for providing greater access to higher education as well as higher earnings for students after graduation. In 2025, Florida Atlantic was nationally recognized as a Top 25 Best-In-Class College and as “one of the country’s most effective engines of upward mobility” by Washington Monthly magazine. Increasingly a first-choice university for students in both Florida and across the nation, Florida Atlantic welcomed its most academically competitive incoming class in the university’s history in Fall 2025. For more information, visit www.fau.edu.
Journal
Harmful Algae
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Productivity, growth, and biogeochemistry of pelagic Sargassum in a changing world
Article Publication Date
28-Aug-2025
